This invention is directed generally to improvements in a cathode ray tube display system of the type used in computer terminals and the like. It is particularly directed to a display system which employs a beam index tube for displaying a color image.
CRT (cathode ray tube) displays which require high resolution may employ a so-called beam index tube. The advantage of such tubes for this application are described in U.S. Pat. No. 4,247,869. Suffice it to say at this juncture that a beam index tube develops an index signal whose timing is indicative of the position of the tube's beam relative to the various phosphor strips on the tube's faceplate. The index signal may, therefore, be used to select and accurately display data at a predetermined location on the faceplate of the tube.
The prior art, and particularly the previously mentioned patent, suggest that the index signal developed by the beam index tube be used for two purposes: to sequentially select successive bits of data for application to the tube, and also to activate a character generator so as to generate the selected data. A disadvantage of such a system is that, by causing the tube to activate the character generator, the character generator is "slaved" to the tube rather than vice versa. Hence, the character generator must be specially designed to mate with the beam index tube. This is undesirable in many situations where it is desired to drive a beam index tube from various types of conventional character generators.